Update submodules: util (new commits)

util:
    a48c210 Chris Smith <chris@dmdirc.com>
            Allow null Files to be passed to TextFile again.

            We do this for temporary configuration files which are never saved
            (e.g. the addon settings). It's a bit of a kludge, but for now we
            should maintain it.

            Fixes-Issue: CLIENT-510
            Gerrit: http://gerrit.dmdirc.com/3507

Change-Id: Ibeaf0b5f996bf8e305dde956906cdd5f3feeb19d